The most common and most likely answer to this crossword clue is the 13 letter word APPA(RE)LLING
I've seen this crossword clue in The Guardian
A
P
P
A
(
R
E
)
L
L
I
N
G
Buddy explains!

The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does APPA(RE)LLING mean?
APPA(RE)LLING verb- To dress or clothe; to attire.
- To furnish with apparatus; to equip; to fit out.
- To dress with external ornaments; to cover with something ornamental
- Clothing